The present invention concerns fluidised bed reactors such as boiler combustion chambers. These reactors consist of a combustion chamber usually made up of tubed membrane walls cooled by a coolant fluid such as a water/steam mixture.
The part of the combustion chamber that can be rectangular is determined by the speed at which the combustion fumes ascend under correct working conditions. Since the periphery of the combustion chamber is fixed, the flow rate of the coolant fluid that can circulate within the wall tubes will be determined according to the diameter and the distance chosen for the said tubes. The height of the combustion chamber allows the thermal exchange surface of the four walls to be obtained, however this height must be optimised with the aim of reducing the height and thus the costs of installation but also in such a way that the time necessary for the chemical reactions between the particles takes place within the combustion chamber.
According to the size of the installation and the required steam cycle, the combustion chamber section forms a perimeter that may be insufficient for the installation into the walls of the tubes in parallel, necessary for the circulation of the quantity of coolant fluid. In addition, the requirement for thermal exchange may necessitate the installation of additional exchange surfaces in the combustion chamber.
One solution already known consists in adding single wall extension panels into the combustion chamber, such as described in patent FR 2 712 378 of the applicant. These extension panels are vertical, tubed and have membranes, and are welded to the periphery walls and fed with coolant fluid in parallel or in series with the walls forming the exterior envelope of the combustion chamber.
However, these single wall extension panels are limited in height, in the number of tubes of which they are composed and in quantity due to the minimum distance required between them, for reasons of stress and erosion by the ashes that circulate within the combustion chamber. The additional exchange surface is thus limited.
These single wall extension panels are heated on both sides by the ashes and the gases which, in certain cases, may result in overheating of the tubes if there should be an imbalance between the thermal flux received from the fluidised bed circulating within the combustion chamber and the flow of coolant fluid that ensures cooling of the tubes.
Another solution could be to increase the height of the combustion chamber in order to increase the exchange surface of the walls without adding internal extensions, but this solution is costly since the overall height of the installation is increased.